When implanting a shoulder prosthesis, it is sometimes necessary to position at the articular end of a patient's scapula a glenoid implant which, on one side, is rigidly anchored in the scapula and which, on the other side, defines an articular surface for cooperation with the head of a humeral implant fixed to the corresponding end of the patient's humerus. In order to anchor the glenoid implant firmly in the scapula, this implant generally comprises a keel projecting from the rest of the implant and intended to be received and immobilized in a canal hollowed out inside the scapula with the aid of an appropriate member, particularly the bit of a surgical drill. When this member is applied on the scapula, an ancillary guiding tool is currently used, which limits the risks of slipping of the stem or tip of this member.
Document U.S. Pat. No. B1-6,379,386 describes such guiding tools. In particular, referring to FIGS. 5 to 9 thereof, this document describes a tool for guiding the bit of a drill, comprising a plate intended to come into surface abutment against the glenoid cavity of a patient's scapula and inside which is formed a central hole for guiding the bit. Thanks to this tool, the surgeon is able to hollow out an incipient canal. This document also describes, with reference to FIGS. 15 to 17 thereof, another tool comprising a plate for abutment on the scapula, inside which are formed three successive guide holes for a bit. The surface of the plate facing towards the scapula is provided with a projection adapted to be housed in the incipient canal previously hollowed out. By successive applications of the drill at the level of each of the three holes, the surgeon disengages a considerable volume of osseous matter and thus hollows out a sufficiently large canal for receiving the keel of the glenoid implant envisaged in this document.
Depending on the patient's morphology, the state of the scapula on which a glenoid implant is intended to be positioned, the operating conditions and/or the exact shape of the implant to be positioned, the longitudinal direction of the canal for receiving the keel of the implant is different. In general, the surgeon should hollow out a canal in the direction where the patient's scapula is the most resistant, particularly in a thick zone where the bone is abundant and healthy.
At the present time, the direction for hollowing out this canal is determined on the scapula either by rule of thumb by the surgeon or, when he is using a tool such as the one described in afore-mentioned document U.S. Pat. No. 6,379,386, is arbitrarily imposed by the plate of the tool used. If the surgeon attempts to apply the drilling member in a chosen direction without using a guiding tool, he runs the risk of the drilling member slipping and/or making a canal in a direction different from the one which he was intending, less favourable for the positioning and subsequent hold of the glenoid implant.
It is an object of the present invention to propose an ancillary tool of simple structure which makes it possible to impose on the drilling, fashioning or like member used during the positioning of a glenoid implant, for example on the bit of a surgical drill, a direction of application chosen by the surgeon, if necessary pre-operatively, over a whole range of possible directions, and even for any anatomically conceivable direction.